1. Field of the Invention
The invention relates to the mineral acid-catalyzed alkylation of hydrocarbons. Specifically, my invention relates to a startup procedure for a hydrofluoric acid-catalyzed alkylation process in which a isoparaffin is reacted with an olefin.
2. Description of the Prior Art
The prior art startup procedure comprises the steps of drying out the plant by the circulation of a dry hydrocarbon stream, charging fresh acid to the plant to provide a dry reaction zone containing the fresh acid, charging an olefin stream to the reaction zone in admixture with the feed hydrocarbon to form the product alkylate and allowing the accumulation of polymers formed as undesired by-products to dilute the acid. This method includes, of course, the normal steps of lining out distillation columns and establishing circulation through the process.
As the strength of the acid decreases due to accumulation of the polymeric diluent, the octane number and end point of the alkylate both improve. As the acid strength decreases to below 90 wt.%, it is standard procedure to begin to pass a slip stream of acid through a regeneration zone in order to maintain the acid strength between 75 and 90 percent (preferably 85-90 percent).
It is well known that olefins, such as butylene or propylene, will readily polymerize when contacted with a catalytic substance such as liquid hydrofluoric acid. The polymerization reaction is in fact so fast that major efforts have been directed toward moderation in order to produce a uniform product as described in U.S. Pat. No. 2,436,929. Likewise, U.S. Pat. No. 2,384,136 describes a method whereby the polymerization of gaseous olefins may be controlled in an alkylation process.
The olefinic feed stream to an alkylation process has been contacted with the liquid catalyst for purposes other than the conditioning of the catalyst. For instance, in U.S. Pat. No. 2,450,039, the location of a double bond in an unsaturated paraffin is shifted to form beta olefins from alpha olefins. In U.S. Pat. No. 2,387,162, the catalyst and an olefin are brought together in such a manner that reactions are limited to the creation of simple olefin-catalyst addition products such as alkyl fluorides. The object of this is the reduction of undesirable side reactions such as polymerization and the promotion of hydrogen transfer shift reactions which yield desired alkylation products after the olefin stream is admixed with a paraffinic stream.